#include<stdio.h>
#include<stdlib.h>
#define MAX 375         //factorial of 200 has 375 digits

/*
    Name        : Rasesh Mori
    Roll        : 201105518
    Assignment  : 0
    Input       : Number for which factorial is to be found (0<=n<=200)
    Ouput       : Factorial of the input number
    Description : Case 1: input<9(i.e. factorial value can be stored in integer variable)
                  * Find factorial by multiplying all the numbers till the number

              Case 2: input>=9
                  * Store the result in an array such that each array variable stores one digit of output and simulate multiplication
*/


int main()
{
    int factorialNum=1; //number of which factorial is to be found
    int counter;
    int factorialValue; //stores result if can be accomodated in integer range
    int factArray[MAX]; //stores factorial of large numbers
    int index;
    int carry = 0;      //used to store carry for multiplication in array
    int arrayValue;     //temporary storage of calculation
    int prefixZeroFlag = 1; //used while printing final answer to remove initial zeroes


    //Get input
    printf("\n Enter number for which factorial is to be found: ");
    if(scanf("%d",&factorialNum) == 0)
    {
        printf("\n\nInvalid input: Please enter an integer in range [0-200]\n\n");
        return 1;
    }


    //Check for correctness of input
    if(factorialNum < 0)
    {
        printf("\n\nFactorial for negative number is undefined.\n\n");
        return 1;
    }
    else if(factorialNum > 200)
    {
        printf("\n\nSorry. This program is designed to find factorial for numbers <= 200.\n\n");
        return 1;
    }



    //If result can be accomodated in integer, use traditional method.
    if(factorialNum < 9)
    {
        factorialValue = 1;

        for(counter = 1; counter <= factorialNum; counter++)
        {
            factorialValue *= counter;
        }
        printf("\nFactorial of %d is: %d",factorialNum, factorialValue);
    }
    else    //Perform multiplication storing each digit in array
    {
        index=MAX-1;
        factArray[index] = 1;

        //initialize array to 0
        for(counter=0; counter < MAX-1; counter++)
        {
            factArray[counter]=0;
        }


        for(counter=2; counter<=factorialNum; counter++)
        {
            while(index>=0)
            {
                arrayValue = factArray[index] * counter + carry;    //Perform multiplication adding previous carry, of any

                carry=0;
                if(arrayValue <= 9)
                {
                    factArray[index] = arrayValue;
                }                           //If result >9, calculate carry and use in next mul.
                else
                {
                    factArray[index] = arrayValue % 10;
                    carry = arrayValue / 10;
                }
                index--;
            }

            carry=0;
            arrayValue=0;
            index=MAX-1;
        }


        printf("\nFactorial of %d is: ",factorialNum);

        for(index=0;index<MAX;index++)                      //Printing result
          {
            if(factArray[index]==0 && prefixZeroFlag)
                continue;
            else
            {
                prefixZeroFlag=0;
                printf("%d",factArray[index]);
            }

        }
    }

    printf("\n\n");
    return 0;
}